Case hardening arrangement utilizing high q tuned circuit

ABSTRACT

Heating pulses are applied to body to be case hardened through a heating inductor coupled to a high Q tuned circuit through a low resistance, low inductance coupling loop. Tuned circuit is pulsed by high energy pulse. Short fall time of pulse causes increased self-cooling. A photoelectric arrangement indicates when body is properly positioned relative to heating coil and initiates heating pulse. Suitable heating inductor construction and arrangement for preventing voltage breakdown between heating inductor and body to be case hardened are described.

United States Patent [191 Frungel 5] Apr. 23, 1974 1 1 CASE HARDENINGARRANGEMENT UTILIZING HIGH Q TUNED CIRCUIT [76] Inventor: Frank Frungel,Glockenocker 2,

' Zurich, Switzerland 7 [22] Filed; Oct. 24, 1972 211 Appl. No; 300,287

[30] Foreign Application Priority Data Feb. 12, 1972 Germany 22068163,259,527 7/1966 Beggs 148/165 2,930,724 3/1960 Rudd.... 148/1503,398,444 8/1968 Nemy 148/165 2,462,903 3/1949 Romander 219/10753,118,999 l/1964 Dreyer 219/1075 3,622,138 11/1971 Kostyal 266/5 E1,909,982 5/1933 Parker 219/1079 X 2,482,493 9/1949 King 219/1077 XPrimary Examiner-Bruce A. Reynolds Attorney, Agent, or Firm-Michael S.Striker 5 7 ABSTRACT Heating pulses are applied to body to be casehardened through a heating inductor coupled to a high Q tuned circuitthrough a low resistance, low inductance coupling loop. Tuned circuit ispulsed by high energy pulse. Short fall time of pulse causes increasedselfcooling. A photoelectric arrangement indicates when [56] ReferencesCited body is properly positioned relative to heating coil and UNITEDSTAT S PATENTS initiates heating pulse. Suitable heating inductor con-3,637,970 1/1972 Cunningham 219/10.75 Struetion and arrangement forpreventing voltage 3,375,468 3/ 1968 Porterfield 219/10.75 breakdownbetween heating inductor and body to be 2,799,760 7/1957 Fruengel219/1075 case hardened are described 2,416,172 2/1947 Gregory et a1219/1077 3,403,241 9/1968 Kauffman 2l9/l0.79 46 Claims, 7 DrawingFigures 16 r 220 21 f 1 I PATENTEU APR 2 3 I974 FIGA ZYIIIIIIIIIIIIIIAFIG.7

CASE I-IARDENING ARRANGEMENT UTILIZING HIGH Q TUNED CIRCUIT BACKGROUNDOF THE INVENTION The present invention relates to methods andarrangements for creating very hard surfaces having an extremely finelygrained structure on metal bodies and particularly on steel. Theso-created surfaces are highly corrosion resistant. More particularly,it relates to methods and arrangements for case hardening steelstructures or bodies by means of applied pulsed high frequencyoscillations, wherein the pulses have a very steep trailing edge and thepulse duration is generally less than 0.1 second. As criteria for thesteep, trailing edge a fall time of less than 1 percent of the pulseduration has proved to yield proper results.

It is known that carbon steels and particularly modern martensiticsteels can be case hardened by use of a rapidly applied high heat whichheats the steel to a temperature as close to the melting point aspossible, the application of said heat being followed by self coolingresulting from the heat conductivity of the body being case hardened. Bysuch methods and arrangements hardnesses of 64Rc have been reached.However, use of conventional high frequency generators has to dateresulted in a surprisingly low efficiency.

The present invention constitutes an improvement of the known method andarrangement which improves said efficiency and results in an improvedproduct of having increased hardness.

SUMMARY OF THE INVENTION The present invention comprises an arrangementfor case hardening of a metallic body.

In particular, the present arrangement comprises high frequencyoscillator means having a high Q tuned circuit means and low internalimpedence amplifier means connected to said high Q tuned circuit means.It comprises pulsing means for pulsing said high frequency oscillatormeans and terminating means for terminating said pulsing of said highfrequency oscillator means after a predetermined heating time interval.Further comprised are heating inductor means forapplying heat to apredetermined portion of the surface of said body. Low resistance, lowinductance coupling loop means couple said high frequency oscillatormeans to said heating inductor means.

In a preferred embodiment of the present invention the heating timeinterval is less than 0.1 second. The pulse of less than 0.1 secondcreated by said pulsing and terminating means has a F all time less than1 percent of the pulse width. This results in a high utilization of theself-cooling effect in carbon steels.

The novel features which are considered as characteristic for theinvention are set forth in particular in theappended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a circuit diagram of aninduction heater in accordance with the present invention;

FIG. 2 shows wave forms at selected points of the circuit of FIG. 1;

FIG. 3 shows an arrangement for initiating the pulses in the circuit ofFIG. 1;

FIG. 4 shows the construction of a heating inductor suitable for use inthe circuit of FIG. 1;

FIG. 5 shows a heating inductor partially surrounded by ferritematerial;

FIG. 6 shows an arrangement for terminating the pulses generated in thearrangement of FIG. I; and,

FIG. 7 shows a curve of heating current as a function of time using thearrangement of FIGS. 1 and 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

A preferred embodiment of the present invention will now be describedwith reference to the drawing.

FIG. 1 shows a circuit in accordance with the present invention. A knownhigh freuqency oscillator with a frequency for example in the regionbetween 20 and 40 MHz is used. However, the Q of the oscillator must bemuch higher than that used in conventional generators employed, forexample, in the welding of plastic sheeting. The Q of the circuit shouldbe at least and may for example be in the range of between 100 and 300.The high Q was found to be necessary afterexperimentation withconventional high frequency oscillators showed surprisingly poor resultswhen used for the case hardening of a body in accordance with thepresent invention. This may'be explained as follows: the inductivity ofthe heating inductor is only of the order of several nH. Thus when sucha heating inductor is introduced into the tuned circuit'of conventionaltype, its inductivity is only an extremely small fraction of the totalinductivity of the circuit, thus allowing only a small percentage of thetotal energy to become available at the surface of the body. Thus, thepresent induction hardening apparatus must be of extremely large sizeand is commercially unfeasible. Use of a tuned circuit with a very highQ, for example a Q of 100 and an oscillator power of IOkW can result ina l MVA oscillation in the tuned circuit. When the heating inductor issupplied from a tuned circuit with such a high reactive power, a veryhigh degree of utilization of the available power can be achieved. Inorder to achieve such a'high degree of utilization, a small couplingloop is introduced into the oscillating cavity of the high Q circuit,andthe actual heating inductance is connected in parallel to this couplingloop. A tuning capacitor of high capacity is connected in parallel tothe two inductors in-order that an exact resonant frequencycorresponding to the resonant frequency of the main oscillating circuitcan be achieved. Reference numeral 1 in FIG. I indicates a cavityresonator having a very high O. For example the cavity may have a volumeof one quarter cubic millimeter and may be constructed from coppersheeting with possibly some silver plating. The cavity is tuned by meansof an air condenser 2 to a convenient frequency, for example 27.l2 MHz.The cavity resonator is supplied by an oscillator tube 3 herein alsoreferred to as amplifier means in conventional fashion, the anode oftube 3 being connected to the circuit via a coupling capacitor 4.Feedback is achieved by means of a small loop 5, a conventional gridcapacitor 6 and grid resistance 7.

It is now possible to directly apply rectangular pulses to the anode oftube 3, via, for example, choke 8, or alternatively, a specialdifferential pulse transformer may be used. The primary winding 10, thesecondary winding 9 and the iron core 11 are comprised in this pulsetransformer. A small, low inductance capacitor. 12 serves toshort-circuit the high frequencies. Also shown in FIG. I is the sourceof electrical energy 15, and connected in parallel thereto a highcapacitance capacitor 13 which is connected in series with the primarywinding of the pulse transformer and also with electronic switch means(first switch means) 14. Switch means 14 may be a large thyristor, anignitron or even a conventional switch. When switch 14 changes from thenonconductive to the conductive state, capacitor 14 discharges throughprimary winding 10, causing a current as shown in curve a of FIG. 2 toflow through primary winding 10. This current in turn causes a voltageproportional to the first derivative thereof to appear across secondarywinding 9. This voltage is shown in curve b in FIG. 2. Since the rate ofincrease of current is substantially linear, a substantially rectangularinduced voltage pulse b results. It thus becomes possible to operatewith very high operating voltages, for example, l0,000 volts at theanode of tube 3. For such high operating voltages no semiconductorswitching means such as thyristors are available at the current state ofthe art. Thus if it is desired that a thyristor be used for switching,the circuit location in the primary circuit of the transformer as isshown for element 14 is very desirable. Here the thyristor does notundergo potential differences of more than one kV, but is subjected tovery high currents. Thus, the thyristor need only have an operatingvoltage of 1,000 volts, while capacitor 13 under these conditions has100 times the capacity but is charged to only l/lO of the voltage ofcapacitor 12. The charging of capacitor '13 from the stabilized voltagesource 15 must take place sufficiently rapidly so that the capacitor ischarged in time for the next subsequent heating pulse. Since theso-required rate is approximately pulses per second, such circuits arewell known and their constructions present no difficulty.

As mentioned above, it is desired in accordance with the presentinvention that the oscillations generated in the tuned circuit 12 aresupplied to the heating inductor with a high efficiency. For thispurpose, the coupling loop 16, which has a low resistance and a lowinductivity, is inserted into the resonant cavity 1. The Q of the tunedcircuit and the geometry of the insertion of the coil are interrelated.The higher the circuit Q, the smaller must be the surface enclosed byloop 16 within tank circuit 1. The enclosed area of labelled 16a in FIG.4. Heating inductor 17 is connected in parallel with coupling loop 17and positioned very closely to the surface of the body.

The circuit including the heating inductor is tuned via a capacitor 18,which may for example be a ceramic capacitor, to approximately theoscillating frequency of the high frequency oscillator. The exactfrequency adjustment is carried out by means of a trimming capacitor 19connected in parallel with capacitor 18. Capacitor 19 may be a parallelplate air capacitor. Under these conditions reactive powers of up to lMVA or more can appear in the tuned circuit comprising elements 16, 17and 18. Under such high reactive powers, voltage in the order ofkilovolts can appear across the heating inductor loop 17 which may undersome conditions comprise only a single small straight section of wire ora single small loop. Under such conditions voltage breakdown between theloops of inductor l7 and the body to be case hardened may be preventedby use of an insulating foil 21 positioned either between the body andthe heating inductor or actually pasted around the body. Foils with atemperature characteristic extending to 1200C are commerciallyavailable. Use of such foils enables very high hardening temperatures tobe generated at the surface of the body 20 while still maintainingadequate electrical insulation.

It is further possible to cool the body by means of blown carbon dioxideor nitrogen, or, for lower requirements, air and for higherrequirements, argon, the appropriate gas being blown in the direction ofarrow 22. This movement of gas also removes ions which may have formedin the air. Thus in this case the blown air does not serve primarily forthe cooling of the surface, but serves for the removal of ions which areformed during the time of the pulse and through which a voltagebreakdown can take place. Care must be taken that the velocity of gas 22is very high. It may for example be necessary to use Laval nozzles foroperating near the velocity of sound. When such rapidly flowing gas isused, the cooling effected by the gas is of the same order of magnitudeas the self-cooling which results through the internal heat conductivityof the body 20 and takes place in the direction of arrows 23 in FIG. 1.

It has also been found rather surprisingly that plain tap water has avery high breakdown characteristic for the short pulses employed in thisinvention. The breakdown strength is approximately 200 killivolt percentimeter. Thus, instead of the gas indicated at reference numeral 22,the surface of the body can be insulated relative to inductor 17 by useof streaming water and, in particular, plain tap water. In this caseisolating foil 21 is not required. The insulating effect of water isapproximately the same as could be obtained by the use of air at apressure of approximately 7 atmospheres between the body 20 and theinductor 17. The cooling effect of the water is here a secondary effect,the primary purpose of the water being the insulation.

Of course, if it is desired to manufacture an extremely oxidation-freesurface, a cooling medium other than water can be used. For examplemethanol which has strongly reducing characteristics and leaves a smoothmetallic surface after hardening may be employed. Use of propane,hydrogen or methane as cooling medium applied in the direction of arrow22 will also prevent tarnishing of the surface. It must be stressed thatin no case can the self-cooling due to the thermoconductivity of theobject itself be dispensed with. In general, carbon steel has a heatconductivity which is at least I000 times that of a good cooling gas. Itis, of course, important for the manufacture of the so-called whitelayers (very hard surfaces) that not only does a spontaneous heating toa very high temperature to just below melting point take place but alsothat after the application of the heating pulse a very rapid coolingtakes place. This can in practice only be obtained due to theself-cooling of the object, although of course the gas or the liquiddescribed above can be an additional aid.

It should further be noted that the cooling by water or oil or methanolcan further result in a slight product improvement when layers of 0.2millimeter thickness are to be hardened. In this case pulses having arelatively long pulse width of approximately 10 millisecends are used.When such wide pulses are used, the self-cooling effect is stronger forthe layers which are more internal to the body, while the very externallayers of the heated surface remain hot longer since the heated layersunderneath prevent the rapid conduction of heat from the outer surfacetowards the interior of the object. Thus, it has been found bymeasurement that the outer layers are actually less hardened than theinner layers, so that the additional cooling of the outer surfaces undermoving air, gas or liquid will aid in the hardening of these outersurfaces. Then a uniform hardness can be reached for a thickness of from0.2 to 0.3 millimeters. For example, hardnesses of 950 kp/mm over awhole hardened section can be achieved in the production of band sawsfrom carbon steel. Further, the method of the present invention does notrequire the subsequent heating that is usual in spontaneous quenchingprocesses to prevent embrittlement, since the so-manufactured layers arevery elastic and not subject to failure by brittleness. Thus, furtherthermal treatment is not required. The case hardened structuresmanufactured in accordance with the present invention are so stable thatmicroscopic observation shows that they decompose into the martensiticbase material only after an application time of approximately six hoursand at a temperature of 450C.

To increase the production speed, it is of course desirable to have thebody to be hardened either rotated steadily or moved past the heatingcoil at a definite rate and to initiate the pulse when the body iscorrectly positioned relative to heating inductor 17. Here a circuit asshown in FIG. 3 can be used. Reference numeral 30 in that Figure refersto a neon-helium laser of the conventional type which sends a fine beam31 through the body 32 which may, for example, be the toothed profile ofa saw. The beam impinges upon a photodiode 33 j which transforms it intoan electrical signal which in per second can be used and an averageanode loss of only 2 kW results. The peak anode voltages may rangebetween 10,000 and 15,000 volts and the reactive power in the tunedcircuit may reach 5 MVA.

Further shown in FIG. 1 is a special circuit arrangement for permittingthe initial tuning of the circuit. A switch 24 is shown whereby theanode of tube 3 may be connected directly to the output of therelatively low voltage source through a resistance 25. Under suchconditions the tuned circuit only contains about one one-hundredth ofits normal power. In order to effect the correct tuning, a small antenna26 is positioned near the tuned circuit comprising elements 16, 19 and17. This antenna may, for example, comprise a small length of wire 26connected to a glow lamp 27 and having at the other side of the glowlamp an additional length of wire as a counterweight. The circuit isthen tuned for maximum brightness of the glow lamp, thereby assuringthat it is properly tuned when full power is applied.

Particularly good results may be obtained when the resonant frequency atthe heating inductor is trimmed in such a way that the full resonance isonly available when the Curie temperature and higher temperatures arereached on the surface of the body. It is known that steel has a highpermeability below the Curie temperature, while having only apermeability comparable to air above the Curie temperature. Thus, thetuning described above may be carried out by using a body of copper orother substance having a low ferromagnetic permeability. In this way,the full power of the heating pulse is not applied to the body at thebeginning of the pulse, that is in the first few microseconds thereof.However, during the remainder of the pulse width, and at crossing of theCurie temperature, a spontaneous and very sudden increase in the heatingresults, since as soon as the Curie temperature is passed, the circuitis correctly tuned to convert the reactive power almost completely intoreal power. In accordance with the present invention it is veryimportant that the trailing edge of the pulse is very steep (i.e. thatthe fall time is very short); under the above conditions a heatingimpulse of substantially needle shape results which causes the hardeningof a particularly thin surface, the exact depth of which may bedetermined in accordance with the equation for the depth of penetrationof high frequency signals into steel. If a hardening to a depth deeperthan such a thin layer (which may only be several thirty thousandths ofa millimeter) is desired, then pulses having a longer width, forexample, 50 millisec onds, may be employed and the conductivity of thebody causes a corresponding deeper layer for example 0.2 millimetersfrom the surface, to be heated also.

FIG. 4 shows a particular preferred embodiment of the heating inductor.The inductor itself in this particular embodiment is a hollow tube witha very thin opening 41 which may have substantially conical terminations42 which in turn are adjacent to the jaws of the contact clamp 43. Ahigh pressure pipe 44. which is situated within the jaws 43 can be usedfor supplying the high pressure water required for cooling. Clamp 43 maycomprise two flat conducting portions which are rigidly clamped togetherand whose inner surfaces 19a and 19b are insulated from each other by athin dielectric 40. The contact clamp can be so designed that capacitiesof an order of magnitude of pF are realized so that capacitors 19 or 18may be smaller capacitors than would otherwise be required. Because ofconical portions 42 the inductors, if damaged or destroyed, may beeasily interchanged. The water under high pressure flows in thedirection of the arrow 45 through the bore 41 and flows out in thedirection of the arrow 46. Either distilled water or tap water which isfree of lime may be used. The pressure to be used here should be morethan the pressure of three atmospheres, and preferably as high as 40atmospheres, while the pipe used for inductor 17 may be very thin, asfor example 2/10 mm. A good material for the manufacture of theinductors is silver piping. Surprisingly, drawn steel tubing can also beused if it is copper plated and if possible also silver plated. Ofcourse, the higher the velocity of the cooling medium the higher thepulse rate that may be used and correspondingly, the higher the thermalrequirements set for inductor 17.

It is of course desirable that the power available in inductor 17 betransferred to the body to the greatest extent possible. For thispurpose the inductor may be surrounded in part by a ferrite material 47as shown in FIG. 5. Commercial high frequency ferrites are availablewhich have permeabilities of the order of magnitude of 600 to 1500 and,therefore, represent a substantial magnetic shortcircuit of the airspace which lies outside of the body. Thus the body 20 can be heatedwith very high field strength and at very low losses even throughinsulating foil 21. If the correct type of magnetic material 47 ischosen, a decrease in permeability for increasing currents in inductorl7, and a corresponding decrease of inductivity can be achieved, whilefor decreasing currents in inductor 17 the permeability can increase.All manufacturers of such ferrite materials furnish curves ofpermeability versus magnetization. When the Curie temperature is passedat that portion of the surface which is being hardened, causing anincrease in the real power and a decrease in the reactive power, thenthe permeability of the material 47 will inv crease. Thus thepermeability of the ferrite material 47 compensates for the change inpermeability in the body resulting from the passing of the Curietemperature, thereby allowing approximately the same power to be appliedto said body both below and above the Curie temperature.

Because of variations in the body to be casehardened, it is oftendifficult to maintain the optimum hardening temperature in massproduction runs. For this purpose the circuit of FIG. 6 may be used. Thebody to be casehardened hereis a saw having reference numeral 20.Inductor I7 is to harden a predetermined portion of the surface of thesawteeth. The loops of the inductor may enclose the teeth of the sawfrom each side, one loop on each side. As the blade of the saw movespast the inductor, the arrangement of FIG. 6 is used to terminate thepulse. In this case the circuit is adjusted in such a manner that thepulse is merely initiated by the circuit of FIG. 3 and has a pulse widthwhich is arbitrarily chosen to be longer than the maximum desired pulsewidth. The pulse is to be terminated by electronic terminating meanswhich, for example, may comprise means connected in parallel with theoscillator circuit for shortcircuiting the latter when the desiredtemperature is reached, thereby preventing any energy from reachinginductor 17. The switch means (herein referred to as second switchmeans) may, for example, be an ignitron or a high voltage thyratron.Referring again to FIG. 6, the heat waves which emanate from the body 20are focused onto a photodiode 54 via a lens 52 and a filter 53. Thephotocell 54 is connected in series with a resistance 56 and a battery55 in the conventional fashion. The pulses resulting when the sofocusedheat waves strike photodiode 54 are amplified by an amplifier 57 whichmay for example be a threshold amplifier which furnishes a pulse on line58 to the control grid of a thyratron 59 (FIG. 1), whenever the voltageat its input exceeds a predetermined threshold voltage. It will be notedthat thyratron 59 has an anode connected to the anode of the oscillatortube 3 via a choke 8 and a cathode connected to ground. Thus when thethyratron becomes conductive it substantially shortcircuits the highfrequency oscillator thereby absorbing the energy that would normally befurnished thereto and thereby preventing this energy from reachinginductor 17. The pulse is thus actually shortcircuited by thyratron 59prior to the natural termination thereof. If a hydrogen thyratron isused which has a current carrying capacity of more than 300 amps and canwithstand peak voltages of to kV, it can readily be accomplished thatthe remaining current of the pulse is completely absorbed by thethyratron instead of the oscillator tube. Filter 53 may, for example, bea light blue filter which emits light only after the predeterminedportion of the surface of the body has reached a temperature of more tha1200C. When this temperature is reached, which is the particulartemperature regarded as an optimum hardening temperature, then a veryrapid rise in current in photodiode 54 results and the pulse is abruptlyterminated at the correct temperature, regardless of the structure ofthe body. It is simply required that a small but representative part ofthe heated portion of the body in FIG. 6) is correctly focused throughthe optical arrangement onto the photodiode 54. A great selection offilters 53 is available in the present state of the art. Orange, greenand blue filters are available, so that the correct filter for a desiredtemperature is readily found.

The heating pulse is again shown in FIG. 7. At time a the pulse starts,for example, initiated by the circuit of FIG. 3 in conjunction withthyristor 14. The pulse would normally have a trailing edge as picturedin curve b. However, because of the temperature measured by photocell54, thyratron 59 is ignited at time c, so that the pulse decreases tozero vary rapidly at time c which of course preceeds the time at whichit would normally collapse. It is further possible to introduce delaymeans following amplifier 57 so that thyratron 59 is not fired until atime d following the reception of the heat pulse at time c. In thiscase, a selected amount of time can elapse, so that the body (workpiece)is heated to a greater depth than would be the case if the pulsecollapsed immediately at the time that the outermost surface reached thedesired temperature.

It is seen that the use of a circuit such as that shown in FIG. 6 inconjunction with a shortcircuiting switching element such as thyratron59 very readily decreases the trailing edge of the heating pulse afterthe correct temperature has been reached. As stated above the switchingelement used need not be a thyratron. High voltage ignatrons as well asother components may be used.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency oscillator means having a high Q tunedcircuit means and low internal impedance amplifier means connected tosaid tuned circuit means; pulsing means for applying a substantiallyrectangular pulse to said high frequency oscillator means over adetermined heating interval, said pulsing means comprising first switchmeans for initiating said pulse and second switch means for terminatingsaid pulse; heating inductor means for applying heat to a predeterminedportion of the surface of said body; and low resistance, low inductancecoupling loop means for coupling said heating inductor means to sai highfrequency oscillator means.

2. An arrangement as set forth in claim 1, wherein said predeterminedheating interval is a time interval of less than 0.l second.

3. An arrangement as set forth in claim 1, further comprising ferritematerial partially enclosing said heating inductor means, said ferritematerial having a permeability exceeding 100 and low high frequencylosses at frequencies higher than MHz.

4. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency oscillator means having a high Q tunedcircuit means including cavity resonator means and low internalimpedance amplifier means connected to said tuned circuit means; pulsingmeans connected to said high frequency oscillator means for initiatingthe oscillations thereof and terminating said oscillations after adetermined heating interval of less than 0.1 seconds; heating inductormeans for applying heat to a predetermined portion of the surface ofsaid body; and low resistance, low inductance coupling loop meansextending into the cavity of said cavity resinator means for couplingsaid heating inductor means to said high frequency oscillator means.

5. An arrangement as set forth in claim 4, wherein said coupling loopmeans extends into the cavity of said cavity resonator means for adistance corresponding to said-Q of said tuned circuit means.

6. An arrangement as set forth in claim 5,, wherein said O of said tunedcircuit means exceeds 100.

7. An arrangement as set forth in claim 6, wherein said cavity resonatormeans comprise copper sheeting enclosing a volume of approximately onequarter cubic meter.

8. An arrangement as set forth in claim 4, further comprising tuningcapacitor means connected in parallel with said heating conductor meansand said coupling loop means.

9. An arrangement as set forth in claim 8, wherein said tuning capacitormeans comprise variable capacitor means.

10. An arrangement as set forth in claim 9, wherein said variablecapacitor means comprise parallel plate air capacitor means.

11. An arrangement as set forthin claim 10, further comprising circuitmeans for operating said high frequency oscillator means at decreasedpower during initial adjustment; further comprising glow lamp meanspositioned near said heating inductor means, meximum glow of said glowlamp indicating correct adjustment of said tuning capacitor means.

12. An arrangement as set forth in claim 4, further comprisingelectrical insulating means insulating said metallic body from saidheating inductor means.

13. An arrangement as set forth in claim 4, further comprising means forblowing gas under pressure through the space between said body and saidheating inductor means, for removing of ions formed therebetween.

14. An arrangement as set forth in claim 13, wherein said gas isnitrogen.

15. An arrangement as set forth in claim 13, wherein said gas is air.

16. An arrangement as set forth in claim 13, wherein said gas is argon.

17. An arrangement as set forth in claim 13, wherein said means forblowing gas comprise Laval nozzles.

1 18. An arrangement as set forth in claim 4, further comprising liquidinsulating means flowing between said body and said heating inductormeans, said liquid insulating means having a breakdown voltagesubstantially higher than that of air.

19. An arrangement as set forth in claim 18, wherein said breakdownvoltage of said liquid insulating means is at least seven times that ofair.

20. An arrangement as set forth in claim 18, further comprising reducingmeans flowing between said body and said heating inductor meanssimultaneously with said liquid insulating means.

21. An arrangement as set forth in claim 20, wherein said reducing meanscomprise methanol.

22. An arrangement asset forth in claim 20, wherein said reducing meanscomprise liquid hydrocarbon.

23. An arrangement as set forth in claim 18, wherein said liquidinsulator means further constitute means for cooling the outermostsurface of said body.

24. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency oscillator means having a high Q tunedcircuit means and low internal impedance amplifier means connected tosaid tuned circuit means; pulsing means coupled to said high frequencyoscillator means for initiating the oscillations thereof and forterminating said oscillations after a determined heating interval, saidpulsing means comprising electronic switch means having a controlelectrode and having a conductive state in response to a control signalat said control electrode, connected to said high frequency oscillatormeans in such a manner that said switch means shunt said high frequencyoscillator means when in a conductive state, thereby terminating saidoscillations; heating inductor means for applying heat to apredetermined portion of the surface of said body; low resistance, lowinductance coupling loop means for coupling said heating inductor meansto said high frequency oscillator means; and control signal furnishingmeans for furnishing said control signal to said switch means at the endof said heating interval.

25. An arrangement as set forth in claim 24, wherein said control signalfurnishing means comprise temperature measuring means measuring thetemperature of said predetermined portion of said surface of said bodyand furnishing said control signal when said someasured temperature is apredetermined temperature.

26. An arrangement as set forth in claim 25, further comprising delaymeans interconnected between said control signal furnishing means andsaid control electrode of said electronic switch means.

27. An arrangement as set forth in claim 26, wherein said delay meanscomprise adjustable delay means.

28. An arrangement as set forth in claim 24, wherein said electronicswitch means comprise thyratron means.

29. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency oscillator means having a high Q tunedcircuit means and low internal impedance amplifier means connected tosaid tuned circuit means; pulsing means coupled to said high frequencyoscillator means for initiating the oscillations thereof and forterminating said oscillations after a determined heating interval;heating inductor means for applying heat to a predetermined portion ofthe surface of said body; low resistance, low inductance coupling loopmeans coupling said heating inductor means to said high frequencyoscillator means; and ferrite material partially enclosing said heatinginductor means, said ferrite material having a permeability exceedingand low high frequency losses at frequencies higher than l5MHz.

30. An arrangement as set forth in claim 29, wherein said ferritematerial comprises material having a decreasing permability in responseto increasing magnetization thereof.

31. An arrangement as set forth in claim 29, wherein said permeabilityof said ferrite material increases when the temperature at said selectedportion of said surface of said body reaches the Curie temperature.

32. An arrangement as set forth in claim 31, wherein said increase ofpermeability of said ferrite material compensates for the decrease ofpermeability of said body upon reaching said Curie temperature.

33. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency oscillator means having a high Q tunedcircuit means and low internal impedance amplifier means connected tosaid tuned circuit means; pulsing means coupled to said high frequencyoscillator means for initiating the oscillations thereof and forterminating said oscillations after a determined heating interval;heating inductor means for applying heat to a predetermined portion ofthe surface of said body, said heating inductor means comprising thin,hollow metal pipe means having a first and second conical termination;low resistance low inductance coupling loop means coupling said heatinginductor means to said high frequency oscillator means; contact clampmeans having conical jaws for receiving said conical terminations ofsaid metal pipe means; and means for circulating high pressure liquidcooling means through said contact clamp means and said metal pipemeans.

34. An arrangement as set forth in claim 33, wherein said contact clampmeans comprise first and second contact clamp means respectivelyreceiving said first and second conical termination, said first andsecond contact clamp means each having an inner surface closely spacedto the corresponding inner surface to the other of said contact clampmeans; further comprising insulator plate means positioned between saidsofacing inner surfaces, for effecting electrical insulationtherebetween.

35. An arrangement as set forth in claim 34, wherein said first andsecond contact means and said insulator plate means form electricalcapacitance means having a high capacity.

36. An arrangement asset forth in claim 33, wherein said high pressureliquid cooling means comprises water.

37. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency oscillator means having a high Q tunedcircuit means and low internal impedance amplifier means connected tosaid tuned circuit means, said tuned circuit means comprising cavityresonator means; pulsing means coupled to said high frequency oscillatormeans for initiating the oscillations thereof and for terminating saidoscillations after a determined heating interval; heating inductor meansfor applying heat to a predetermined por- 12 tion of the surface of saidbody; and low resistance low inductance coupling loop means for couplingsaid heating inductor means to said high frequency oscillator means,said coupling loop means extending into the cavity of said cavityresonator means.

38. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency 0scillator means having a high Qtunedcircuit means and low internal impedance amplifier means connectedto said tuned circuit means; pulsing means coupled to said highfrequency oscillator means for initiating the oscillations thereof andfor terminating said oscillations after a determined heating interval,said pulsing means comprising energy storage means, pulse transformermeans having a secondary winding connected to said high frequencyoscillator means and a primary winding,

and first switch means for connecting said primary winding of said pulsetransformer means to said energy storage means when in a conductivestate; heating conductor means for applying heat to a predeterminedportion of the surface of said body; and low resistance low inductancecoupling loop means for coupling said heating inductor means to saidhigh frequency oscillator means.

39. An arrangement as set forth in claim 38, wherein said energy storagemeans comprise capacitor means.

40. An arrangement as set forth in claim 39, wherein said first switchmeans comprise thyristor means.

41. An arrangement as set forth in claim 40, wherein the discharge ofenergy from said capacitor means through said primary winding of saidpulse transformer means creates a current through said pulse transformermeans having a substantially constant rate of increase with respect totime, thereby creating a substantially rectangular voltage across saidsecondary winding of said pulse transformer means.

42. An arrangement as set forth in claim 41,- wherein said thyristormeans has a gate, said thyristor means having a conductive state inresponse to a voltage at said gate; further comprising means applyingsaid voltage to said gate when said body is correctly positionedrelative to said heating inductor means.

43. An arrangement as set forth in claim 42, wherein said means applyingsaid voltage to said gate comprise photoelectric means.

44. An arrangement as set forth in claim 43, wherein said photoelectricmeans comprise a light source; and photoelectric transducing meansreceiving light from said light source intermittently in dependence onthe position of said body relative to said heating inductor means.

45. An arrangement as set forth in claim 44, wherein said light sourceis a neon-helium laser.

46. An arrangement as set forth in claim 45, wherein said photoelectrictransducing means is a photodiode.

1. Arrangement for casehardening of a metallic body, comprising, incombination, high frequency oscillator means having a high Q tunedcircuit means and low internal impedance amplifier means connected tosaid tuned circuit means; pulsing means for applying a substantiallyrectangular pulse to said high frequency oscillator means over adetermined heating interval, said pulsing means comprising first switchmeans for initiating said pulse and second switch means for terminatingsaid pulse; heating inductor means for applying heat to a predeterminedportion of the surface of said body; and low resistance, low inductancecoupling loop means for coupling said heating inductor means to saidhigh frequency oscillator means.
 2. An arrangement as set forth in claim1, wherein said predetermined heating interval is a time interval ofless than 0.1 second.
 3. An arrangement as set forth in claim 1, furthercomprising ferrite material partially enclosing said heating inductormeans, said ferrite material having a permeability exceeding 100 and lowhigh frequency losses at frequencies higher than 15 MHz.
 4. Arrangementfor casehardening of a metallic body, comprising, in combination, highfrequency oscillator means having a high Q tuned circuit means includingcavity resonator means and low internal impedance amplifier meansconnected to said tuned circuit means; pulsing means connected to saidhigh frequency oscillator means for initiating the oscillations thereofand terminating said oscillations after a determined heating interval ofless than 0.1 seconds; heating inductor means for applying heat to apredetermined portion of the surface of said body; and low resistance,low inductance coupling loop means extending into the cavity of saidcavity resinator means for coupling said heating inductor means to saidhigh frequency oscillator means.
 5. An arrangement as set forth in claim4, wherein said coupling loop means extends into the cavity of saidcavity resonator means for a distance corresponding to said Q of saidtuned circuit means.
 6. An arrangement as set forth in claim 5, whereinsaid Q of said tuned circuit means exceeds
 100. 7. An arrangement as setforth in claim 6, wherein said cavity resonator means comprise coppersheeting enclosing a volume of approximately one quarter cubic meter. 8.An arrangement as set forth in claim 4, further comprising tuningcapacitor means connected in parallel with said heating conductor meansand said coupling loop means.
 9. An arrangement as set forth in claim 8,wherein said tuning capacitor means comprise variable capacitor means.10. An arrangement as set forth in claim 9, wherein said variablecapacitor means comprise parallel plate air capacitor means.
 11. Anarrangement as set forth in claim 10, further comprising circuit meansfor operating said high frequency oscillator means at decreased powerduring initial adjustment; further comprising glow lamp means positionednear said heating inductor means, meximum glow of said glow lampindicating correct adjustment of said tuning capAcitor means.
 12. Anarrangement as set forth in claim 4, further comprising electricalinsulating means insulating said metallic body from said heatinginductor means.
 13. An arrangement as set forth in claim 4, furthercomprising means for blowing gas under pressure through the spacebetween said body and said heating inductor means, for removing of ionsformed therebetween.
 14. An arrangement as set forth in claim 13,wherein said gas is nitrogen.
 15. An arrangement as set forth in claim13, wherein said gas is air.
 16. An arrangement as set forth in claim13, wherein said gas is argon.
 17. An arrangement as set forth in claim13, wherein said means for blowing gas comprise Laval nozzles.
 18. Anarrangement as set forth in claim 4, further comprising liquidinsulating means flowing between said body and said heating inductormeans, said liquid insulating means having a breakdown voltagesubstantially higher than that of air.
 19. An arrangement as set forthin claim 18, wherein said breakdown voltage of said liquid insulatingmeans is at least seven times that of air.
 20. An arrangement as setforth in claim 18, further comprising reducing means flowing betweensaid body and said heating inductor means simultaneously with saidliquid insulating means.
 21. An arrangement as set forth in claim 20,wherein said reducing means comprise methanol.
 22. An arrangement as setforth in claim 20, wherein said reducing means comprise liquidhydrocarbon.
 23. An arrangement as set forth in claim 18, wherein saidliquid insulator means further constitute means for cooling theoutermost surface of said body.
 24. Arrangement for casehardening of ametallic body, comprising, in combination, high frequency oscillatormeans having a high Q tuned circuit means and low internal impedanceamplifier means connected to said tuned circuit means; pulsing meanscoupled to said high frequency oscillator means for initiating theoscillations thereof and for terminating said oscillations after adetermined heating interval, said pulsing means comprising electronicswitch means having a control electrode and having a conductive state inresponse to a control signal at said control electrode, connected tosaid high frequency oscillator means in such a manner that said switchmeans shunt said high frequency oscillator means when in a conductivestate, thereby terminating said oscillations; heating inductor means forapplying heat to a predetermined portion of the surface of said body;low resistance, low inductance coupling loop means for coupling saidheating inductor means to said high frequency oscillator means; andcontrol signal furnishing means for furnishing said control signal tosaid switch means at the end of said heating interval.
 25. Anarrangement as set forth in claim 24, wherein said control signalfurnishing means comprise temperature measuring means measuring thetemperature of said predetermined portion of said surface of said bodyand furnishing said control signal when said so-measured temperature isa predetermined temperature.
 26. An arrangement as set forth in claim25, further comprising delay means interconnected between said controlsignal furnishing means and said control electrode of said electronicswitch means.
 27. An arrangement as set forth in claim 26, wherein saiddelay means comprise adjustable delay means.
 28. An arrangement as setforth in claim 24, wherein said electronic switch means comprisethyratron means.
 29. Arrangement for casehardening of a metallic body,comprising, in combination, high frequency oscillator means having ahigh Q tuned circuit means and low internal impedance amplifier meansconnected to said tuned circuit means; pulsing means coupled to saidhigh frequency oscillator means for initiating the oscillations thereofand for terminating said oscillations after a determined heatinginterval; heating inductor means for applying heat to a predetermineDportion of the surface of said body; low resistance, low inductancecoupling loop means coupling said heating inductor means to said highfrequency oscillator means; and ferrite material partially enclosingsaid heating inductor means, said ferrite material having a permeabilityexceeding 100 and low high frequency losses at frequencies higher than15MHz.
 30. An arrangement as set forth in claim 29, wherein said ferritematerial comprises material having a decreasing permability in responseto increasing magnetization thereof.
 31. An arrangement as set forth inclaim 29, wherein said permeability of said ferrite material increaseswhen the temperature at said selected portion of said surface of saidbody reaches the Curie temperature.
 32. An arrangement as set forth inclaim 31, wherein said increase of permeability of said ferrite materialcompensates for the decrease of permeability of said body upon reachingsaid Curie temperature.
 33. Arrangement for casehardening of a metallicbody, comprising, in combination, high frequency oscillator means havinga high Q tuned circuit means and low internal impedance amplifier meansconnected to said tuned circuit means; pulsing means coupled to saidhigh frequency oscillator means for initiating the oscillations thereofand for terminating said oscillations after a determined heatinginterval; heating inductor means for applying heat to a predeterminedportion of the surface of said body, said heating inductor meanscomprising thin, hollow metal pipe means having a first and secondconical termination; low resistance low inductance coupling loop meanscoupling said heating inductor means to said high frequency oscillatormeans; contact clamp means having conical jaws for receiving saidconical terminations of said metal pipe means; and means for circulatinghigh pressure liquid cooling means through said contact clamp means andsaid metal pipe means.
 34. An arrangement as set forth in claim 33,wherein said contact clamp means comprise first and second contact clampmeans respectively receiving said first and second conical termination,said first and second contact clamp means each having an inner surfaceclosely spaced to the corresponding inner surface to the other of saidcontact clamp means; further comprising insulator plate means positionedbetween said so-facing inner surfaces, for effecting electricalinsulation therebetween.
 35. An arrangement as set forth in claim 34,wherein said first and second contact means and said insulator platemeans form electrical capacitance means having a high capacity.
 36. Anarrangement as set forth in claim 33, wherein said high pressure liquidcooling means comprises water.
 37. Arrangement for casehardening of ametallic body, comprising, in combination, high frequency oscillatormeans having a high Q tuned circuit means and low internal impedanceamplifier means connected to said tuned circuit means, said tunedcircuit means comprising cavity resonator means; pulsing means coupledto said high frequency oscillator means for initiating the oscillationsthereof and for terminating said oscillations after a determined heatinginterval; heating inductor means for applying heat to a predeterminedportion of the surface of said body; and low resistance low inductancecoupling loop means for coupling said heating inductor means to saidhigh frequency oscillator means, said coupling loop means extending intothe cavity of said cavity resonator means.
 38. Arrangement forcasehardening of a metallic body, comprising, in combination, highfrequency oscillator means having a high Q tuned circuit means and lowinternal impedance amplifier means connected to said tuned circuitmeans; pulsing means coupled to said high frequency oscillator means forinitiating the oscillations thereof and for terminating saidoscillations after a determined heating interval, said pulsing meanscomprising energy storage means, pulse transformer means having asecondary winding connected to said high frequency oscillator means anda primary winding, and first switch means for connecting said primarywinding of said pulse transformer means to said energy storage meanswhen in a conductive state; heating conductor means for applying heat toa predetermined portion of the surface of said body; and low resistancelow inductance coupling loop means for coupling said heating inductormeans to said high frequency oscillator means.
 39. An arrangement as setforth in claim 38, wherein said energy storage means comprise capacitormeans.
 40. An arrangement as set forth in claim 39, wherein said firstswitch means comprise thyristor means.
 41. An arrangement as set forthin claim 40, wherein the discharge of energy from said capacitor meansthrough said primary winding of said pulse transformer means creates acurrent through said pulse transformer means having a substantiallyconstant rate of increase with respect to time, thereby creating asubstantially rectangular voltage across said secondary winding of saidpulse transformer means.
 42. An arrangement as set forth in claim 41,wherein said thyristor means has a gate, said thyristor means having aconductive state in response to a voltage at said gate; furthercomprising means applying said voltage to said gate when said body iscorrectly positioned relative to said heating inductor means.
 43. Anarrangement as set forth in claim 42, wherein said means applying saidvoltage to said gate comprise photoelectric means.
 44. An arrangement asset forth in claim 43, wherein said photoelectric means comprise a lightsource; and photoelectric transducing means receiving light from saidlight source intermittently in dependence on the position of said bodyrelative to said heating inductor means.
 45. An arrangement as set forthin claim 44, wherein said light source is a neon-helium laser.
 46. Anarrangement as set forth in claim 45, wherein said photoelectrictransducing means is a photodiode.